In generic internal combustion engines, the turbocharger is used to obtain energy from the exhaust gas of the piston-cylinder unit(s) and convert it into compression work for the propellant-air mixture supplied to the piston-cylinder unit(s). An adjustment of the ignition timing is used to influence the position of center of gravity of the combustion in the individual piston-cylinder units of the internal combustion engine.
The combustion center of gravity means the state in which half of the fresh charge is combusted and is expressed by the corresponding crankshaft angle. This is also known as MFB 50, i.e. 50% of the mass fraction burned (MFB). For the terms, reference is made to textbooks on internal combustion engines. See, in particular, Heywood, John B., Internal Combustion Engine Fundamentals, New York, McGraw-Hill, 1988.
The combustion center of gravity influences the combustion efficiency of the internal combustion engine and the amount of emissions generated.
It is also known that the power of the internal combustion engine can be regulated via targeted flushing of exhaust gases around the exhaust turbine of the turbocharger by means of the variable opening degree of a wastegate. This is also evident from U.S. Pat. No. 4,496,286 A. By increasing the opening of the wastegate, an increased free flow cross-section is offered to the exhaust gases of the piston-cylinder units, whereby the exhaust-gas pressure against which the pistons of the piston-cylinder units must work is lowered.
A disadvantage of this is that the mentioned regulating operations (change of the ignition timing and change in the opening degree of the wastegate) influence the different degrees of efficiency of the internal combustion engine individually, namely the combustion efficiency (also referred to as “high-pressure efficiency” in the literature) and the load change efficiency (referred to as “low-pressure efficiency” in the literature).